The main objective of antenna processing techniques is to utilize the spatial diversity which consists in using the position of the antennas of the network to better utilize the differences in incidence and in distance of the sources.
One of the technical problems to be solved in this field is that of the location of transmitters consisting in determining their coordinates, which will be envisaged in 2 dimensions or 2D, in the plane and/or in 3 dimensions or 3D, in space, on the basis of measurements of AOA and/or TDOA type. Multi-transmitter location requires a transmitter-based association of the parameters of AOA/TDOA type, hence joint estimation of the AOA/TDOA parameters.
The field of AOA estimation in the presence of multi-transmitters and multi-paths on the basis of a multi-channel receiving station is very vast. That of TDOA estimation is just as wide as that of AOA with in particular the techniques according the prior art. However, most of the time the measurement is performed on the basis of two signals arising from two single-channel stations. These techniques are then not very robust in multi-transmitter or multi-path situations. This is why the prior art proposes TDOA techniques making it possible to separate the sources on the basis of a priori knowledge about their cyclic characteristics.
AOA/TDOA joint estimation has generated a large number of references such as described in the prior art. These works are much more recent than the previous ones on TDOA and are due essentially to the advent of cellular radio-communications systems as indicated explicitly in documents of the prior art. Unlike the previous references for TDOA, the processes are performed with multi-channel receiving stations. However, the objective is to carry out the parametric analysis of a multi-path channel from a single transmitter E1 to a multi-channel receiving station at A1. The jointly estimated parameters are then the angles of arrival θ11j and the time deviations τ11j−τ11j′ between the paths of this same transmitter due to reflectors at Rj and Rj′. This kind of system does not make it possible to carry out the location of the transmitter at E1 such as is envisaged in FIG. 1, unless the positions of the reflectors at Rj and Rj′ are known. The joint estimation of the parameters (θ11j, τ11j−τ11j′) is very often envisaged on the basis of the knowledge of a pilot signal such as the TSC sequence codes (Training Sequence Code) for GSM (Global System Mobile) or the spreading codes for signals of CDMA (Code Division Multiple Access) type.
TOA (Time Of Arrival) estimation techniques have been envisaged for locating mobiles in cellular radio-communications systems and for locating radio-navigation receivers of GPS/GALILEO type for the Global Positioning System. These estimation techniques are performed on the basis of the knowledge of a pilot signal and can be carried out with multi-channel receiving stations. Location often requires the demodulation of transmitted signals which returns, for example, the position of the satellites in GPS/GALILEO and allows location of the receiver on the basis of the knowledge of the position of the satellites as well as the estimation of the TOA on each of the satellites. The TOA estimation and location techniques then require an accurate knowledge of the operation and characteristics of the radio-navigation or radio-communications system but they do not make it possible to carry out location in the general case without a priori knowledge of system type or of signal type.
The location of a transmitter on the basis of the AOA/TDOA parameters has spawned a significant bibliography. These data processing techniques are generally suited to mono-transmitter situations and sometimes envisage problems with tracking when the transmitter is in motion or else one of the receiving stations is intentionally in motion. In this field numerous references use Kalman filtering. However, these location techniques do not deal with the case of TDOA measurements performed on asynchronous receiving stations. In the prior art the authors propose a direct estimation of the position of the transmitters on the basis of the set of signals originating from all the reception channels of all the stations. In this paper, the authors deal with the problem of multi-sources through algorithms known from the prior art. It directly estimates the positions of the transmitters through an antenna processing approach. However, it assumes that all the signals have the same bandwidth and that the signals originating from the various stations are synchronous. This approach does not, however, make it possible to deal with the problem of the multi-paths generated by reflectors and the problem of asynchronism between the various stations.